A conventional PON system and an OLT used as a station apparatus in the PON system will be described with reference to FIGS. 10 and 11.
When connecting a plurality of ONUs to a carrier network (service network), an optical splitter is arranged in the PON section, and the ONUs are connected to one OLT, as shown in FIG. 10.
In the conventional PON system, an OLT as shown in FIG. 11 is used. Referring to FIG. 11, a first transmission/reception circuit 52 is a circuit that transmits/receives a frame to/from an ONU via the PON connected to a PON port 51.
A second transmission/reception circuit 58 is a circuit that serves as an interface to a carrier network NW connected via an SNI port 59.
A frame demultiplexing unit 53 is a processing unit that transmits, out of upstream frames input from the first transmission/reception circuit 52, a frame (control frame used to control the PON) for the OLT to a control frame processing unit 54 and transmits the remaining frames to a frame transfer processing unit 60.
A frame multiplexing unit 56 is a processing unit that time-divisionally multiplexes a downstream frame from the frame transfer processing unit 60 and a control frame from the control frame processing unit 54 and transmits them to the first transmission/reception circuit 52.
The frame transfer processing unit 60 is a processing unit that transfers frames received from both the frame demultiplexing unit 53 and the second transmission/reception circuit 58 based on their destination MAC addresses and the like.
The control frame processing unit 54 is a processing unit that performs processes concerning PON control such as a discovery process for automatically assigning an LLID to each ONU and arbitration of an upstream signal (signal from an ONU to the OLT) and processing of transferring PON-IF port information such as the LLID of each ONU to a band assignment processing unit 55.
The band assignment processing unit 55 is a processing unit that performs assignment of a band (transmission start time and transmission data amount) to an ONU or management of PON-IF port information transferred from the control frame processing unit 54 in response to a request from the control frame processing unit 54.
Data are exchanged using a frame having the arrangement as shown in FIG. 12 in the PON section of the PON system, that is, the section between an ONU n and the OLT.
Referring to FIG. 12, the preamble is formed by embedding an LLID in the preamble of Ethernet®.
The LLID (Logical Link ID) is an identifier provided in a one-to-one correspondence with each ONU.
The LLID is decided by the OLT when registering an ONU (placing an ONU under the OLT). The OLT manages the LLIDs without repetition among the ONUs under it.
A VLAN tag is a tag including VLAN information. The tag may be absent, or a plurality of tags may be added. The VLAN tag includes TPID and TCI.
TPID (Tag Protocol ID) is an Ether Type value representing that a VLAN tag follows. The value is normally 0x8100.
TCI (Tag Control Information) is VLAN tag information. The TCI includes PCP, CFI, and VID.
PCP (Priority Code Point) is the priority of the frame.
CFI (Canonical Format Indicator) is a value representing whether the MAC address in the MAC header complies with the standard format.
VID or VLAN ID (VLAN Identifier) is a value that designates a VLAN to which the frame belongs.
Type is an Ether Type value representing the type of the host protocol. In some cases, notation “Type/Length” or the like is used because the area is also used for a Length value.